Heretofore, as a die used in extrusion molding of honeycomb, there has been known the die for extrusion molding of honeycomb, provided with groovy slits on the front face thereof which are formed by cell blocks, and provided with puddle inlets on the back face thereof which are communicatively connected with the slits.
In such a die for extrusion molding of honeycomb, for the purpose of adjusting the slit widths between the respective cell blocks and enhancing the durability of the dies, for example, a surface treatment is performed along the line of forming a nickel plating layer (a first coating film) of 10 to 70 μm on the surface of a cell-block body, and then forming, on the surface of the nickel plating layer, either a composite plating layer in which hard powders of SiC, diamond, CBN, or the like is dispersed in the nickel plating layer or a tungsten carbide layer of 5 to 15 μm (a second coating film).
However, in the case where a tungsten carbide film is formed in the above described surface treatment, it is difficult to adjust the film thickness as compared with the plating, and accordingly there has been a problem that dimensional error is caused for the dies in which the target dimension±2 μm is required for the coating film (a first coating film+a second coating film).
The above described tungsten carbide film is easily liable to vary in a ratio of W and C, and a frictional resistance with puddle being extruded varies due to a variation of the ratio; accordingly, when a difference in a frictional resistance distribution in the formed film is large, the molding comes to be unstable, and the shapes of the molded bodies are hardly made stable, and hence the rate of good quality products has remained low.
Additionally, when the composite plating film is formed in the above described surface treatment, the hard grains are protruded on the composite plate film, and the coefficient of the friction with puddle being extruded varies depending on the hard grain density; thus, when the hard grain density distribution difference is large, there has occurred a fact that the molding comes to be unstable, and the shapes of the molded bodies are hardly made stable, and hence the rate of good quality products is lowered.
Furthermore, as for the above described die for extrusion molding of a honeycomb, puddle is made to flow partially, in order to adjust the dimensional dispersion of the die before the extrusion molding of a honeycomb.
However, in the case where a tungsten carbide film, a titanium based film, or a composite plating film is used for the second coating film, there has been a problem that the adjustment of the die is difficult and accordingly takes a long time because these films are hard.
The present invention is achieved in view of the above described problems heretofore, and takes as its object the provision of a die for extrusion molding of a honeycomb which is possible to eliminate the dimensional error of the die, maintain a stable frictional force of extrusion, be excellent both in extrusion moldability and in abrasion resistance, and additionally make the adjustment of the die easy at the time of extrusion molding.